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Think of the atom as a tiny solar system: a dense nucleus at the center with electrons moving in fixed paths around it. This planetary picture was refined to explain why light comes in specific colors from atoms. The crucial step was introducing quantized orbits: electrons can only occupy certain allowed paths with particular energies. When an electron jumps from one energy level to another, it emits or absorbs a photon with a precise energy, producing definite spectral lines. This combination of fixed orbits and energy changes in those orbits is what ties the planetary model to this scientist’s work. The other scientists contributed important ideas earlier or later, such as a positively charged sphere with embedded electrons, a nucleus-centered atom without stable planetary orbits, or atoms as indivisible spheres, but the planetary, orbit-based view is the one associated with this figure.